Flexible screen comprising cathodic microtubes

ABSTRACT

A display screen, characterized in that the pixels of the image are generated by individual light-emitting capsules, said capsules constituting miniature cathodic tubes cold-cathode and being assembled in a matrix on a least one substrate of supple support, optionally transparent. The material emitting electrons of the capsules may be constituted by carbon nanotubes. 
     The assembly of the capsules may be realized by forced insertion of the prefabricated capsules into a supple support, with or without previously cutting out placements of the capsules in the supports. Assembly of the capsules may likewise be done by moulding the prefabricated capsules in a supple support. 
     Advantageously, the size of the capsules is optimized to ensure optimum matricial assembly of the pixels or correct balance of the non-printing areas, with for example a larger size for the capsules emitting its green light.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of PCT Application Serial No.PCT/FR2004/00911, filed Apr. 14, 2004, now pending, which claims thebenefit of and priority to French Patent Application No. FR0304897,filed Apr. 19, 2003, all of which are incorporated herein by referencein their entirety.

The subject of the present invention is a flexible display devicewhereof each image point is constituted by one or morecold-cathodoluminescence capsules, these capsules being sealedindividually and assembled by an automated process on a supplesubstrate.

FIELD OF THE INVENTION

The present invention relates to the domain of flat display screenscomprising large-size screens, typically over a metre in diagonal.

Conventionally, such screens comprise an assembly of image elements orpixels, organised in a matrix and addressed by a network of conductorsin rows and by a network of conductors in columns.

SUMMARY OF THE INVENTION

According to the object of the present invention, these display elementsare capsules constituting miniature cold-cathode cathodic tubes, havingfor example one capsule for each colour point of each pixel.

In addition, these capsules are designed to be able to be assembledautomatically and form a flexible screen on a supple substrate, withoutrequiring a complex transfer operation.

The present invention thus describes a display screen, characterised inthat the pixels of the image are generated by individual light-emittingcapsules, said capsules constituting miniature cathodic tubescold-cathode and being assembled in a matrix on at least one substrateof supple support, optionally transparent.

According to a preferred embodiment the material emitting electrons ofthe capsules is constituted by carbon nanotubes.

The assembly of the capsules is preferably realised by forced insertionof the prefabricated capsules into a supple support, with or withoutpreviously cutting out placements of the capsules in the supports.

Assembly of the capsules is preferably likewise done by moulding theprefabricated capsules in a supple support.

Advantageously, the size of the capsules is optimised to ensure optimummatricial assembly of the pixels or correct balance of the non-printingareas, with for example a larger size for the capsules emitting itsgreen light.

According to a preferred embodiment of the present invention, a tactiledetection device, of mechanical, optical, resistive, capacitive or othertype, is put in place at least on one part of the screen, as acomplement to the luminous capsules.

According to one of the embodiments of the present invention, thecapsules are connected and fed by conductive films made from the filmmedia.

For example, the capsules are connected and fed by at least twoconductive films on the films media, one of the films locatedsubstantially at the front side of the screen, on the user side, theother film located substantially on the rear side, opposite the user,the capsules automatically connecting to each film during theirassembly.

According to another embodiment of the present invention, the capsulesare connected and fed by one or more networks of supple metallic hollowwires, optionally organised so that one of the networks connects thetubes in rows perpendicular to the connection rows made by the othernetwork, the connections permitting relative movement of the capsulesamong one another necessary during flexion of the screen.

By way of advantage, at least part of the capsules is equipped with acolour filter, made by tinting the glass of the capsule or by attached acolour film, said filter being optimised for preferentially transmittingthe light spectrum of colour close to the light emitted by the capsuleon which it is mounted.

To facilitate assembly, the capsules of each primary colour of eachimage element can be assembled as a trio prior to being mounted on thesubstrate support.

The invention will be better understood, and other aims, advantages andcharacteristics thereof will emerge more clearly from the followingdescription of preferred embodiments given by way of non-limitingexample and accompanied by a set of diagrams, in which:

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 to 5 are schematic representations of certain embodimentsaccording to the present invention.

DETAILED DESCRIPTION

FIG. 1 schematically illustrates the assembly of cathodoluminescentcapsules 11 on a supple substrate represented here by two flexible films12, 13 supporting the conductive films for addressing and feeding, notshown in this figure. It is understood that it would be an advantage touse only a single flexible film of adequate thickness, carrying anetwork of conductors on each of its faces.

FIG. 2 proposes a schematic section of an individual capsule 21, so asto specify the function and the connection mode:

A sealed glass envelope 22 empty of air contains a cold cathode 24emitting electrons by field effect with respect to luminophorous powder23, a material emitting light when it receives electrons of adequateenergy. A control grid 25, here in annular shape, helps control theemission of electrons by regulating the potential and thus the electricfield in the vicinity of the cathode 24. Such a capsule thus comprisesthree electrodes 26, 27 and 28 respectively connecting the luminophores23, the cathode 24 and the control grid 28. According to the presentinvention, these three electrodes shall be connected automatically,during assembly of the capsules, to the corresponding conductornetworks. For example, the anode contacts 26 of all the tubes couldadvantageously all be connected in parallel to a common conductor planproviding high-voltage continuous feed, while the electrodes 27 and 28shall be traditionally connected in networks in rows and columns.

In the case according to the invention described in the application FR02 13 287 in which each capsule is piloted locally by an addressingmicrocircuit, all the corresponding electrodes of the capsules could beconnected in parallel.

In addition, and according to the invention described in the applicationFR 02 13 285, incorporating a microtransformer into or on each capsulecreates locally the anode voltage, which then also becomes the controlvoltage. Each capsule then has only two external electrodes, those ofthe primary circuit of the microtransformer, to be connected either innetwork in rows and columns, or in parallel by means of addressingmicrocircuits individual to each capsule.

FIG. 3 is a view from the user side of a screen according to anembodiment of the present invention wherein capsules of differentdiameters 31, 32 and 33 are utilised for each colour. Such anarrangement can:

-   -   optimise the relative intensity of each colour and thus provide        a correct blank area,    -   better compose the capsules and thus obtain a large emitting        surface, while conserving a square form preferable for pixels of        the screen.

FIG. 4 is a view from the user side of a screen according to anembodiment of the present invention wherein the capsules 41 areconnected by means of a network of supple metallic wires 42 arranged ina mesh, completed by a network of perpendicular wires 43, capable ofbeing conductive, if all the electrodes are connected in parallel, orinsulating if the aim is to connect the electrodes in one directiononly, in rows or in columns.

FIG. 5 is a sectional view specifying the possible construction of acapsule in such an embodiment:

-   -   the anode contact of the capsule 51 is equipped with a metallic        flange 53, connected by the mesh wires 52, corresponding to the        wires 42 of FIG. 4.    -   the cathode is connected by an electrode in the form of a hook        55 to a second network of conductor wires 54, which could        obviously be perpendicular to the conductors 52, if needed. The        role of the hook is to lock the capsule in place, using the        spring effect resulting from the mechanical tension applied to        the wires 52 and 54, enabling mechanical sliding of the contact        during flexion of the screen.

For each embodiment, it is preferable to include a protectivetransparent film covering the user side of the capsules and sealing theassembly against storms. Similarly, an encapsulation film, which doesnot need to be transparent, will be provided in the rear face.

According to the invention, making a flexible display screen byautomated assembly of individual cathodoluminescent capsules on a supplesubstrate contributes a large number of advantages whereof an example isdescribed hereafter:

-   -   the result is a flexible but reliable screen, from using        miniature rigid and sealed capsules, without having to make        supple light-emitting devices. In fact, the development of such        supple devices, including organic electroluminescent diodes,        encounters difficulties in compatibility of the organic        materials, as well as contamination and degradation, especially        by diffusion of atmospheric gases in the emitting layers.    -   this gives a large-size supple screen at low cost, by optimising        the capsules and their assembly and connection system so as to        eliminate any necessarily costly individual positioning and        transfer system.

To avoid having to sort the capsules of different colours, the capsulescould be grouped as a trio prior to assembly, forming a complete pixelcapable of taking a polarised form facilitating its insertion in theright direction.

According to the assembly mode used, a reparable screen could beproduced, for example to guard against vandalism.

The individual cathodoluminescent capsules effectively all utilise theelectrons emitted, without loss of electrons in the metallic mask or theinter-pixel space as in a cathodic screen or a classic field emissionscreen. The result is considerable luminous efficacy.

It is possible to produce coloured filters by tinting the glass of eachcapsule or by bringing in a colour film, much more easily than for aconventional cathodic tube. Such coloured filters substantially improvethe contrast of the screen when illuminated.

The positioning of the various structural elements lends maximum usefuleffects to the object of the invention, to date not obtained by similardevices.

1. A flexible display screen for displaying a plurality of pixels of animage, said display screen comprising: a flexible support member adaptedto hold at least one display element associated with each said pixel;and feeding means for feeding each said display element, wherein eachsaid display element comprises a capsule, each said capsule forming aminiature cold cathode ray tube including a sealed envelope devoid ofair, an electron-emitting material positioned in an interior portion ofsaid envelope, and a light emitting material positioned in the interiorportion of said envelope and configured to emit light in response toreception of electrons, wherein a plurality of said capsules areconstructed to be arranged in a matrix upon insertion into the flexiblesupport member, and wherein said feeding means includes at least onenetwork of flexible woven metallic wires, said network havingconnections with the capsules, said connections being constructed topermit movement of the capsules relative to one another during flexingof the display screen, wherein said connections comprise a hook.
 2. Theflexible display screen as recited in claim 1, wherein saidelectron-emitting material is constituted by carbon nanotubes.
 3. Theflexible display screen as recited in claim 1, wherein said flexiblesupport is transparent.
 4. The flexible display screen as recited inclaim 1, further comprising: a set of three capsules associated witheach said pixel, each said capsule being provided with a respectivecolor filter.
 5. The flexible display screen as recited in claim 4,wherein said three capsules associated with each said pixel areassembled as a trio prior to being mounted on said support member. 6.The flexible display screen as recited in claim 1, further comprising: atactile detection device positioned on at least one part of the displayscreen and complementing said plurality of capsules.